Cereal-based snack foods are quite popular and may take a variety of specific forms, such as seasoned corn curls, taco chips, tortilla chips, crackers, etc., all of which, usually, require some seasoning at least on the surfaces thereof. That seasoning must be adhered to those surfaces by an edible adhesive, and in the past, that adhesive has most usually been an oil or fat. For example, when a potato chip is produced (potatoes being considered cereal for the purposes of this invention), sliced potatoes are deep fat fried. After removal from the fryer, the potato chips have considerable oil or fat on the surfaces thereof, and when dusted with a seasoning, e.g. salt, the salt adheres to the surfaces of the potato chips by way of a residual fat functioning as an adhesive. Corn chips, such as taco chips and tamale chips, may be likewise produced, but here the seasoning will be a mixture of flavors and, usually, salt. As another example, corn curls and crackers are often flavored with cheese powder. Corn curls, for example, after puffing from dough, may be sprayed with an oil, and then the cheese powder adhered to the surfaces thereof by way of the oil functioning as an edible adhesive. Crackers are usually leavened and baked, and likewise require oil sprayed on the surfaces to function as an adhesive, e.g. an adhesive for seasonings, including cheese powders.
However, for dietary purposes, it is often important to reduce the fat intake, and snack foods, as described above, have been produced with reduced fat contents, the reduction in fat content being both in regard to the fat in the formulations of doughs for forming the snack food and in the fat used in the adhesive for the seasoning. For example, a cracker may be baked with a relatively low fat content, but with that low fat content, sufficient residual fat does not remain on the cracker for adequately adhering seasonings to the surfaces of the cracker. If additional fat is placed on the crackers for adhesive purposes, that additional fat would defeat, to a large measure, the purpose of providing a low fat dough for producing the cracker.
As a result, the art has sought low fat adhesives for snack foods of the nature described above. Various substitutes for the traditional fat adhesives have been proposed in the art. Many of these proposals involve water solutions of various edible ingredients which, when applied and dried on the snack food, provide a tacky adhesive for adhering the seasonings. These approaches, however, suffer from a common difficulty. Since such snack foods are intended to be shelf stable, the moisture content of the snack food (or at least the water activity of the snack food) must be at a low level in order to prevent staling and bacterial growth on the snack food during shipping, handling and storing. It is difficult when applying water solutions of such tackifying adhesives to ensure that the water used for application of the adhesive is sufficiently evaporated to reduce the moisture content of the adhesive (and also the snack food) to a safe level of water activity and one that will not induce staling of the substrate, i.e. snack food. This is particularly true when the adhesive material itself is hygroscopic, which is often the case with edible sugars and alcohols. In addition, such hydroscopic adhesives will absorb moisture, particularly when the snack food package is opened, and the snack food may become sticky or tacky and may allow staling and/or bacterial growth.
While not directed to cereal-based snack foods, the problem discussed above has been a considerable problem in other snack food arts, such as in the art of coating nuts. For example, U.S. Pat. No. 3,477,858 discloses that adhesives, such as starch-based adhesives or gums, tend to flake off and produce unsightly fines. Also, it is disclosed that non-oily adhesives, such as sorbitol and mannitol, have difficulty in that, especially, sorbitol remains tacky for long periods of time, e.g. at least 18 hours, after cooling to room temperature, and the nuts tend to adhere to each other. In addition, sorbitol is hydroscopic and the nuts tend to be sticky after exposure to high humidity. On the other hand, mannitol becomes hard and brittle, immediately after removing the nuts from a molten bath thereof, with poor drainage of the mannitol, agglomeration of the nuts, and difficulties in obtaining an adequately seasoned product. That patent goes on to propose a mixture of mannitol and sorbitol for somewhat mitigating these difficulties.
Somewhat similarly, U.S. Pat. No. 3,671,266 proposes coating nuts with a hexitol, e.g. mannitol, sorbitol and mixtures thereof, wherein at least 10% sorbitol is used.
U.S. Pat. No. 4,161,545 recognizes the above-discussed U.S. Pat. No. 3,671,266, but points out that the approach of that patent produces dark-colored nuts, and instead proposes a mixture of honey and water followed by enrobing with a dry mixture of sugar and starch.
However, U.S. Pat. No. 4,692,342 recognizes the above-described U.S. Pat. No. 4,161,545, but states that improved adhesion of seasoning can be achieved when the nuts are coated with a dry adhesive film-forming material and then with an aqueous mixture of honey and an adhesive film-forming material. Adhesive materials such as vegetable gums, dextrin, modified starches, albuminoids, and the like are suggested.
Somewhat similar problems are also encountered in producing ready-to-eat food bars, e.g. commonly referred to an "granola bars", and in those bars the binders are usually sugar syrups, shortening or the like. However, glycerine had also been proposed as the binder, but as U.S. Pat. No. 4,605,561 points out, in order to keep such food products from spoiling, the water activity (A.sub.W), in general, must be less than about 0.9, and hydroscopic materials can cause difficulties in this regard, especially polyhydric alcohols, such as sorbitol and glycerol. That patent then goes on to propose a fondant of sucrose, corn syrup, fat and water as the binder.
U.S. Pat. No. 4,451,488 points out that the polyhydric alcohols may be used, in such food bars, but used in combination with a binder system that includes sugars, shortening and a combination of sorbitol and glycerol.
Cereal grains involve something of a similar problem, and U.S. Pat. No. 3,806,613, directed to a fortifying coating on cereal grain products, states that adhesive films of gums, shellac and the like have been used in the past for such purposes, but points out that edible fatty acid esters of glycerol or sorbitol provide better results, especially for iron-fortified cereals.
Something of the same problem is also found in connection with dried fruits. For example, U.S. Pat. No. 4,363,825 relates to dried and shredded coconut and points out that glycols, such as propylene glycol, butylene glycol or glycerol, function as humectants for such products, which allow easy rehydration of the shredded coconut. To achieve low moisture content, the patent goes on to propose a coating of glycerol monostearate, glycerol, propylene glycol, maltodextrin, creamed coconut and salt.
As can be, therefore, easily appreciated, the art has recognized a number of difficulties in connection with adhesive coatings and binders for various foods. The specific problems vary, considerably, with the particular food involved, as briefly discussed above, but the common denominator of these difficulties is that of finding adequate materials to function in lieu of the traditional fats, for binding and adhesive purposes, for the particular food involved.
It would, therefore, be of substantial benefit in the art to provide an adhesive for a snack food which has both low fat content, for dietary purposes, and low moisture content, for storage-stable purposes, and which adhesive can adequately adhere seasoning to the surface of a cereal-based snack food, which snack food and the surfaces thereof present their own set of difficulties, especially that of absorption of the adhesive into the snack food itself. At the same time, it would be important to the art to provide such adhesives which are not brittle, such as aqueous applied and dried monosaccharides, i.e. sugars, but on the other hand, are not humectants which can increase water activity on storage, such as polyhydric alcohols. It would be a further advantage to the art to provide such adhesives which will firmly adhere the seasonings, but which will not become tacky and adhere the seasoned pieces of snack food together during handling, storage and use.